You have a choice to click on "use with remote and balance board" or "use with remote only" before you start the game. If you don't feel comfortable doing some exercises on the board then you should not click on "use with board" at first. Not all exercises use the board, but if you click on "use board" and then don't, it will affect your skill points for that exercise. It's best to use the "remote only" until you are comfortable doing the exercises. Of course, some exercises don't use the board and they tell you that before starting that particular exercise.

the board has a limit of 300 pounds but a guy did a video on youtube to show how you can cut foam put under it and weigh up to 330 and still make it work...very good demo too!

I have the game and you have the choice of playing with or without the balance board. I haven't played it with another person yet but I assume all you really need extra is the wii remote unless you want to play with the balance board; then you may need an extra balance board.